1. The Field of the Invention
The present invention relates to the formation of polymers. More particularly, the present invention relates to the synthesis of amorphous polymers formed from .alpha.-olefins that have color and adhesive qualities that are improved over the prior art. In particular, the present invention relates to a continuous, economical amorphous polyolefin synthesis process which includes a reactor design, an olefin monomer and hydrocarbon solvent recycling and purification system, a catalyst deactivation and polymer stabilization system, and a polymer isolation process.
2. The Prior State of the Art
Predominantly amorphous polyolefin solutions can be produced in a solution process using a loop reactor. In a loop reactor, the polyolefin and reactants are continually circulated. The amorphous polyolefins formed are dissolved in unreacted liquid monomer and/or hydrocarbon solvent.
A process was developed to produce dissolved polyoctene in an unreactive mineral spirits solvent. During the catalyst deactivation process, catalyst poisons were being introduced to the system and other catalyst poisons being produced. The process of catalyst deactivation resulted in substantial loss of solvent and unreacted monomer due to poisoning thereof by the effects of the catalyst deactivation compounds. The unreacted monomer and solvent needed to be cleaned of the poisons before they could be recycled.
Attempts were made to reclaim the solvent. These attempts included fractional distillation of the recycled solvent and unreacted monomer through a 25-plate distillation column, followed by circulating the center-cut solvent for 16 hours through an absorption bed train as illustrated in FIG. 1. The result, however, was only poor catalyst productivity of about 30% of a control process. The control process was established by running the polymerization process under the same conditions with the exception that ail feedstocks were provided as fresh off-the-shelf commodities. Under the control conditions, catalyst productivity was established at a nominal 100%. Additionally, the degree of conversion of monomer with the control conditions was in excess of 70%.
Another prior art process for recovering product and deactivating the catalyst entailed introduction of chemicals such as antioxidant, acid scavenger, and catalyst deactivator into a product surge tank and mixing by use of a circulating pump. The product stream after such treatment was then introduced into a screw extruder and the majority of the volatile materials were removed by low-pressure fractionation after catalyst deactivation. The light-key components removed thereby were then distilled and passed through an absorption bed train such as that depicted in FIG. 1. As in the above-mentioned prior art process, use of the distillation column and the absorption bed train was considered expedient because recovery of both unreacted monomer and the solvent were necessary for environmental and economic reasons. Once again, use of recycled monomer and solvent, even after substantial purification through distillation and in the absorption bed train resulted in inferior catalyst productivity, also about 30%, in comparison to the control.
Other difficult tasks included catalyst deactivation in a predominantly polymer mass and isolating polymer such as polyoctene from a 20-40% dissolved polymer solids in a mineral spirits solution. Thus, there existed challenges for developing an economical continuous amorphous polymer synthesis process. These challenges included the redesigning of the reactor, a method for purification of recycled monomer and solvent, a method for catalyst deactivation, and a method for isolation of the amorphous polymer. No commercial processes existed previously for the production of amorphous polyhexene or for amorphous polyoctene having high molecular weight (an inherent viscosity (IV) from about 3 1.0 IV to about 5.0 IV), good color, and good adhesive properties.
Therefore, what is needed in the art is an improved method of producing high molecular weight amorphous polymers. Such features and advantages are disclosed and claimed herein.